This invention relates to cameras having a programmed shutter, and particularly to cameras having a programmed shutter with at least one switch member in an electrical circuit closed by operation of the opening member of the shutter assembly.
In cameras of this type there is generally selected a fixed programmed exposure value for a flash setting. For example, 1/60 seconds exposure is generally utilized in combination with a predetermined lens opening. Flash ignition is triggered by release of the shutter. Since the electrical circuit works simultaneously with the triggering without interruption, a delaying circuit must be provided in the flash device so that the flash discharge does not occur immediately upon releasing the shutter, but after a period of delay. Such a delaying circuit is essential in prior art units. Such units are not fully satisfactory as including such a delaying circuit represents additional expenditure during construction and assembly of the camera. In addition, if one wishes to discharge the flash at different programmed exposure values, it would be necessary to provide a specialized delaying circuit for each such programmed setting. This latter feature would result in yet higher costs of assembly.
In the known cameras including a programmed shutter, the existing light conditions are not measured upon activation of the flash. A predetermined shutter exposure is communicated to the shutter program over a fixed resistor, for example, 1/60 seconds. In a programmed shutter assembly, this exposure time is coupled with a corresponding lens opening for the shutter opening of 1/60 seconds.
In addition to the requirement of a delaying circuit, setting a predetermined shutter time with a fixed resistor is costly. This is the case because the time-measuring photo-electric elements which are usually utilized in measuring daylight exposures without a flash cannot be utilized. Thus, the prior art cameras require incurring double expenses. On the one hand, the delaying circuit must be included and, on the other hand, a circuit for providing the predetermined shutter-time values must also be included.
German Patent Specification DE-AS No. 17 72 768 teaches discharge of the flash during opening of the lens shutter at a time dependent upon the distance setting so that the effective lens opening varies depending on the distance. Herein, the time of discharge is adjusted by a mechanism wherein changing the distance setting on the camera changes the position of a contact piece. During the course of the opening movement of the lens, the current circuit for the flash is closed through physical contact. In this solution, the mechanical parts and mountings and bearing supports must be of utmost precision, since minimal deviation and tolerances will adversely effect the relatively short path between the electrical contacts which are adjustable in response to a change in the distance setting of the camera. Wear and tear to such mechanical parts and the force they are subjected to, as well as dust accumulation adversely effect operation of this type of construction.
In this type of construction, adjusting of the time of the shutter opening depends on the intensity of the light supplied by the flash. The shutter reacts far too slowly to operate with sufficient percision. Accordingly, in practice, the solution proposed by DE-AS No. 17 72 768 cannot be utilized because adjusting of the discharge time, which lies fully within the range of a few milliseconds cannot be sufficiently effected by mechanical displaced elements. In these known mechanical solutions, in most cases, the flash has delivered its discharge of light before the flash-cycle can be interrupted by mechanical means. In other words, these solutions generally provide over-illumination.
A further disadvantage of the known solutions utilizing delaying circuits is illustrated by DA-AS No. 20 08 124. It should be pointed out that the delaying circuits proposed in these publications presuppose that in order for them to function smoothly, that during the entire life time of the camera as well as that of the flash device that the mechanical and electrical elements will run fully synchronized fashion. As a practical matter, such is not the case.
Accordingly, it is desirable to provide a camera including switch mechanisms which overcome the disadvantages of the known arrangements and provide a camera having a programmed shutter with a flash device which will overcome the shortcomings of the prior art. Further it is desirable to provide a camera wherein flash discharge will occur at attainment of a predetermined lens opening, which will depend upon the distance setting. In such a solution, flash discharge is to occur simultaneously with the start of the closing of the opened programmed shutter.